Vapor pressure measuring

Analytical Procedures. Oxygen difluoride may be determined conveniently by quantitative appHcation of k, nmr, and mass spectroscopy. Purity may also be assessed by vapor pressure measurements. Wet-chemical analyses can be conducted either by digestion with excess NaOH, followed by measurement of the excess base (2) and the fluoride ion (48,49), or by reaction with acidified KI solution, followed by measurement of the Hberated I2 (4). 

RVP is a vapor pressure measurement at a fixed air/Hquid ratio of 4 and a temperature of 38°C. It is measured under conditions of water saturation. For samples which contain water-soluble components such as alcohols, ASTM D4953 is used. 

Thermodynamic. The thermodynamic properties of elemental plutonium have been reviewed (35,40,41,43—46). Thermodynamic properties of sohd and Hquid Pu, and of the transitions between the known phases, are given in Table 5. There are inconsistencies among some of the vapor pressure measurements of Hquid Pu (40,41,43,44). 

The molecular composition of sulfur vapor is a complex function of temperature and pressure. Vapor pressure measurements have been interpreted in terms of an equiHbtium between several molecular species (9,10). Mass spectrometric data for sulfur vapor indicate the presence of all possible molecules from S2 to Sg and negligible concentrations of and S q (H)- In general, octatomic sulfur is the predominant molecular constituent of sulfur vapor at low temperatures, but the equihbrium shifts toward smaller molecular species with increasing temperature and decreasing pressure. 

A minimum volatihty is frequently specified to assure adequate vaporization under low temperature conditions. It can be defined either by a vapor pressure measurement or by initial distillation temperature limits. Vaporization promotes engine start-up. Fuel vapor pressure assumes an important role particularly at low temperature. For example, if fuel has cooled to —40°C, as at arctic bases, the amount of vapor produced is well below the lean flammabihty limit. In this case a spark igniter must vaporize enough fuel droplets to initiate combustion. Start-up under the extreme temperature conditions of the arctic is a major constraint in converting the Air Force from volatile JP-4 to kerosene-type JP-8, the military counterpart of commercial Jet Al. 

The activity coefficients of sulfuric acid have been deterrnined independentiy by measuring three types of physical phenomena cell potentials, vapor pressure, and freeting point. A consistent set of activity coefficients has been reported from 0.1 to 8 at 25°C (14), from 0.1 to 4 and 5 to 55°C (18), and from 0.001 to 0.02 m at 25°C (19). These values are all based on cell potential measurements. The activity coefficients based on vapor pressure measurements (20) agree with those from potential measurements when they are corrected to the same reference activity coefficient. 

Hypochlorous acid and chlorine monoxide coexist in the vapor phase (78—81). Vapor pressure measurements of aqueous HOCl solutions show that HOCl is the main chlorine species in the vapor phase over <1% solutions (82), whereas at higher concentrations, CI2O becomes dominant (83). The equihbtium constant at 25°C for the gas-phase reaction, determined by ir and uv spectrophotometry and mass spectrometry, is ca 0.08 (9,66,67,69). The forward reaction is much slower than the reverse reaction. 

Now interpret phase X as pure solute then Cs and co become the equilibrium solubilities of the solute in solvents S and 0, respectively, and we can apply Eq. (8-58). Again the concentrations should be in the dilute range, but nonideality is not a great problem for nonelectrolytes. For volatile solutes vapor pressure measurements are suitable for this type of determination, and for electrolytes electrode potentials can be used. 

The diazirines are of special interest because of their isomerism with the aliphatic diazo compounds. The diazirines show considerable differences in their properties from the aliphatic diazo compounds, except in their explosive nature. The compounds 3-methyl-3-ethyl-diazirine and 3,3-diethyldiazirine prepared by Paulsen detonated on shock and on heating. Small quantities of 3,3-pentamethylenediazirine (68) can be distilled at normal pressures (bp 109°C). On overheating, explosion followed. 3-n-Propyldiazirine exploded on attempts to distil it a little above room temperature. 3-Methyldiazirine is stable as a gas, but on attempting to condense ca. 100 mg for vapor pressure measurements, it detonated with complete destruction of the apparatus." Diazirine (67) decomposed at once when a sample which had been condensed in dry ice was taken out of the cold trap. Work with the lower molecular weight diazirines in condensed phases should therefore be avoided. 

The Eq for the free energy of vaporization of nitric acid for the temp range 275-305°K has been obtained from vapor pressure measurements (Ref 30)... 

Temp, °C Vapor Pressure (mm Hg) according to Eqn No Vapor Pressure Measured, mm Hg (Ref 4c)... 

Two additional points near 17.0 and 20.3 K are required. These may be determined by using either ihe constant volume gas thermometer or by vapor pressure measurements of H . 

It should be emphasized that a survey of the vapor pressure measurements of plutonium-bearing species above bivariant Pu02-x(s) revealed that in general these measurements suffer from a lack of knowledge of the composition of the condensed phase. 

The depression of the activity may be measured in various ways. The most obvious would involve a measurement of the vapor pressure lowering, but this method is superseded by others both in accuracy and in simplicity of execution. The boiling point elevation and freezing point depression methods relegated vapor pressure measurement... 

Fig. 111.—Experimental values of the interaction parameter %i plotted against the volume fraction of polymer. Data for polydi-methylsiloxane M =3850) in benzene, A (New-ingi6). polystyrene in methyl ethyl ketone, (Bawn et aV ) and polystyrene in toluene, O (Bawn et alP) are based on vapor pressure measurements. Those for rubber in benzene, T (Gee and Orr ) were obtained using vapor pressure measurements at higher concentrations and isothermal distillation equilibration with solutions of known activities in the dilute range.

Gee ° has applied this method to the determination of the interaction parameters xi for natural rubber in various solvents. Several rubber vulcanizates were used. The effective value of VelV for each was determined by measuring its extension under a fixed load when swollen in petroleum ether. Samples were then swollen to equilibrium in other solvents, and xi was calculated from the swelling ratio in each. The mean values of xi for the several vulcanizates in each solvent are presented in Table XXXVI, where they are compared with the xi s calculated (Eq. XII-30) from vapor pressure measurements on solutions of unvulcanized rubber in some of the same solvents. The agreement is by no means spectacular, though perhaps no worse than the experimental error in the vapor pressure method. 

Silva and Weber (1993) reported vapor pressure measurements for the 1-ch oro-l,l-Difluoroethane (RI42b) and 1,1 -Difluoroethane (R152a) refrigerants. The data are given in Tables 3.5 and 3.6 respectively. Use Antoine s equation to correlate the data for R142b and the following equation for R152a (Silva and Weber, 1993)... 

Rard (1992) reported the results of isopiestic vapor-pressure measurements for the aqueous solution of high-purity NiCl2 solution form 1.4382 to 5.7199 mol/kg at 298.1510.005 K. Based on these measurements he calculated the osmotic coefficient of aqueous NiCb solutions. He also evaluated other data from the literature and finally presented a set of smoothed osmotic coefficient and activity of water data (see Table IV in original reference). 

The authors would like to acknowledge the contributions of the following researchers J.R. DeBaun and L.S. Mullen-Rokita, for helpful discussions E.B. Cramer, for assisting with the adsorption measurements L.-S. Yu-Farina, for the water solubility and partition coefficient measurements H. Myers, for the vapor pressure measurements and R.R. Winter, for running the MACCS molecular structure analyses. 

Carmona, F.J., Gonzalez, J.A., Carcia de la Fuente, I., Cobos, J.C., Bhethanabotla, V.R., Campbell, S.W. (2000) Thermodynamic properties of n-alkoxyethanols + organic solvent mixtures. XI. Total vapor pressure measurements for n-hexane, cyclohexane or n-hcptanc + 2-ethoxyethanol at 303.15 and 323.15 K. J. Chem. Eng. Data 45, 699-703. 

Morgan, D.L., Kobayashi, R. (1994) Direct vapor pressure measurements of 10 n-alkanes in the C10 - C28 range. Fluid Phase Equil. 97, 211-242. 

Piacente, V., Fontana, D., Scardala, P. (1994) Enthalpies of vaporization of a homologous series of n-alkancs determined from vapor pressure measurements. J. Chem. Eng. Data 39, 231-237. 

Verevkin, S.P. (2004) Vapor pressure measurements on fluorene and methyl-fluorenes. Fluid Phase Equil. 225, 145-152. 

Wieczorek, S.A., Kobayashi, R. (1980) Vapor pressure measurements of diphenylmethane, thianaphthene, and bicyclohexyl at elevated temperatures. J. Chem. Eng. Data 25, 302-305. 

Water vapor pressure measurement in a dosing volume and, later, in the headspace above the equilibrated sample, and... 

From the normal boiling point of isobutyl alcohol (T° = 108.1°C,381.2K p°=760 torr), and one other vapor pressure measurement I found while doing research for this section (T=100°C, 373K p=570 torr), I ve gotten the heat of vaporization (AH), the heat needed to vaporize a mole of pure isobutyl alcohol itself. Using these two values in the Clausius-Clapyron equation, the AH for isobutyl alcohol is 10039.70 cal/mole. 

FIG. 14 Illustration of the vapor pressures measured in an a measurement. The vapor pressure in both the water and the food containers is established by macroscopic diffusion of water out of the sample (pure water or food). 

Daubert, T. E., Jones, D. K. Project 821 Pure component liquid vapor pressure measurements. AIChE Symp. Ser., 86. 1990 pp. 29-39. 

As a means of verifying the model parameters of Table II, the osmotic coefficient was calculated from isopiestic vapor pressure measurement data (17) for the KCl-KBr-H20 system at 25°C (Table III). 

Vapor Pressure Measurements and Data Processing by Thermogravimetry/... 

Knudsen cells (effusion cells) are exclusively used for vapor pressure measurements (see vapor pressure) in the pressure range from 1 torr to 10-6 torr. In the low temperature range (—20° — +400 °C) pyrex glass cells are applicable. Especially the vapor pressures of dyes, organic compounds can be measured in such cells, because metal cells may sometimes cause catalytic decompositions of the investigated materials. 

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